Drifting tubing

ABSTRACT

A method of checking for restrictions in a string of tubing formed of a plurality of tubing sections. The method involves providing a profile in the tubing string, providing a drift member adapted to engage with the profile, passing the drift member through the tubing string, and determining whether the drift member has engaged with the profile prior to separating the tubing sections.

FIELD OF THE INVENTION

This invention relates to drifting tubing; that is, the process ofdetermining whether the bore of a length of tubing is restricted orobstructed.

BACKGROUND OF THE INVENTION

In the oil and gas exploration and production industry long strings ofjointed tubing or pipe are utilised to carry fluids between the surfaceand downhole locations within drilled bores, which strings and bores maybe several kilometres long. In all downhole operations there is a smallpossibility of the pipe bore becoming restricted by, for example, cementresidue or foreign objects such as a piece of wood or a metal bolt. Inmost cases this does not have any detrimental effect on operations.However, there are numerous tools and procedures that require a ball,dart or plug to travel through the pipe to perform a specific functiondownhole. Accordingly, prior to such operations it is necessary toinspect the pipe for the presence of any restrictions which would holdup the ball, dart or plug. Such inspections are normally achieved bychecking the pipe string in stages as the string is pulled out of thebore and the pipe sections are separated at surface, before beingreassembled in preparation for the operation involving the passage ofthe ball, dart or plug. Pipe strings are normally formed of largenumbers of pipe sections that are typically around 10 metres long andhave threaded ends. The pipe sections are often made up and stored as“stands”, each formed of three pipe sections, and thus around 30 metreslong. Accordingly, when a pipe string is being pulled out of a bore, thestring is lifted in 30 metre stages, to allow the uppermost stand to beremoved.

One other commonly used method of checking the pipe bore forrestrictions is to drop a hollow sleeve, of a slightly larger diameterthan the ball, sleeve or plug, on a 40 m length of wire into the upperend of the pipe string. The pipe string is then pulled out of the boreto allow removal of the top pipe stand. If the wire is visible when thestand is separated from the string the operator knows that the sleeve isin the next stand and that the stand that has been separated from thestring is unobstructed. This operation may be carried out relativelyrapidly, but on many occasions the sleeve will not drop through thepipe, and the wire may become tangled or drop down such that it is notvisible when the stand is separated. Thus, the drift and the obstructionpoint may go unnoticed.

In another method, an operator working at an elevated level simply dropsan object, or drift, of a slightly larger diameter than the ball, sleeveor plug, through each pipe stand as it is being racked. The drift isretrieved at the bottom of the stand and then returned to the operatorby means of the elevators used to lift the pipe out of the bore. Thisprocess is relatively slow, and it is not unknown for the drift to bedropped or otherwise fall, at significant risk to operators workingbelow.

BjØrnstad U.S. Pat. No. 6,581,453 teaches a method of drifting pipewhere the drift includes a radio transmitter or radioactive source. Thedrift is used in conjunction with a detection device positioned atsurface to locate the position of the drift inside the drillpipe as thepipe is pulled from the hole. Such electronic detection of a drift hasthe drawback of being somewhat complicated, and the equipment wouldrequire to be physically robust. The equipment would also have to beintrinsically safe so as not to provide an ignition source If the driftincorporated a radioactive source, regulations would require the driftto be handled and stored with great care. BjØrnstad also teaches a 30mlong drift in the form of a Ripe that will be detected by default as thepipe is pulled from the hole. However, it is believed that theconsiderable weight of the drift and other issues would pose significantpractical difficulties for an operator.

Polley U.S. Pat. No. 4,452,306 describes apparatus for detectingruptures in drill pipe above and below the drill collar. The apparatusis deployed in response to surface loss in drilling pressure, indicativeof washout in the drill pipe. The apparatus comprises a tool that may bepumped down through a drill pipe string to seat in a sub in the drillstring above the drill collars. The drill pipe string is thenpressurised above the tool to a predetermined pressure and the pressureheld for a predetermined time. The pressure is monitored and, if thepressure holds, any rupture in the drill pipe is below the tool. If thepressure holds, the pressure in the string above the tool is increasedto shear pins in the tool, allowing an actuator within the tool body tomove and expose by-pass apertures. This allows fluid to drain fromstring as the string is retrieved to permit drill pipe repair below thedrill collars. If, on the other hand, the drill pipe does not holdpressure above the tool, the drill pipe is pulled one section at a time.The stands are checked until the drill pipe washout is located. Thedamaged pipe is replaced and the drill string is tested again. If thepressure holds, the pressure is increased until the pins shear, to allowcirculation through the tool. The tool may then be retrieved onwireline.

Morrill U.S. Pat. No. 5,343,946 describes a drop-in check valve used tore-establish control of a well in circumstances where there may be a gasbuild-up downhole. The valve is pumped from surface to lock into alanding sub provided in the string close to the bottom of the hole. Thevalve includes a ball that is pushed against a seat when the downholepressure exceeds the pressure above the valve.

It is among the objectives of embodiments of the present invention toprovide an efficient, technically simple and safe method for driftingtubing.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method ofchecking for restrictions in a string of tubing comprising a pluralityof tubing sections, the method comprising:

providing a profile in the tubing string;

providing a drift member adapted to engage with said profile;

passing the drift member through the tubing string; and

determining whether the drift member has engaged with said profile priorto separating the tubing sections.

The invention also relates to apparatus for identifying the presence ofa bore restriction in a tubing string, the apparatus comprising a driftmember adapted to pass through tubing and to engage a profile in thetubing bore, the engagement of the drift member with the profile beingoperator detectable.

The tubing may be located in a hole or bore, and will typically take theform of a tubing or pipe string. If the tubing profile is locatedtowards the distal end of the tubing, the passage of the drift memberthrough the tubing to engage the profile identifies to the operator thatthe tubing does not contain any restrictions which would prevent passageof the member, such that the tubing string may then be retrieved withouthaving to carry out any further checks for the presence of restrictions.In other embodiments it may be desired to run a ball, dart or plugthrough the tubing without first retrieving the tubing string, and thepassage of the drift member through the tubing to engage the profileidentifies to the operator that the ball, dart or plug will be free topass through the tubing to its intended location. In this case, thedrift member is preferably retrievable, and to this end may be providedwith a fishing neck of the like. Of course if the drift member fails toengage the profile this indicates to the operator that the ball, dart orplug would be unable to pass through the tubing and the tubing must thenbe cleared or retrieved for inspection.

The method may further include the step of identifying the diameter of aball, dart, plug or other device to be passed through the tubing andselecting a drift member of similar diameter; typically, a drift memberwill be selected which defines a diameter or dimension only slightlylarger than the device. Thus, in some cases, the drift member will notidentify minor restrictions in a length of tubing, which would notaffect the passage of the device. This avoids unnecessary inspection oftubing for restrictions, which would not impact on the passage of thedevice.

Preferably, the drift member is adapted to be pumped through the tubing.The member may thus travel relatively quickly and positively through thetubing, and will not be reliant solely on gravity to pass through thetubing, reducing the likelihood of the member stopping in the tubingother than when the member encounters a substantial restriction. Thedrift member may incorporate fins, which may be flexible, to facilitatein translating the member through the tubing, or the member may beotherwise configured to assist in moving the member reliably through thetubing.

Preferably, the drift member is adapted to permit fluid flowtherethrough, for example the member may be in the form of a sleeve.Thus, even with the drift member engaged with the profile, or engagedwith a restriction, fluid may pass through the member. This permitsfluid to drain from the tubing through the member and, if necessary, forfluid to be passed through the tubing. In certain embodiments, the driftmember may have a configuration adapted to prevent or significantlyrestrict fluid flow: the member may incorporate a burst disc or the likewhich initially serves to occlude the tubing, but which may be removedor otherwise opened. One advantage offered by such an arrangement isthat, if the drift member encounters a restriction, the location of therestriction may be determined by identifying the volume of fluid thathas been pumped into the tubing behind the drift member when the memberencounters the restriction. Thus, when the tubing string is beingretrieved, it will not be necessary to check for restrictions untilreaching the anticipated location of the drift member in the string.

In one embodiment of the invention, a first drift member adapted topermit fluid flow therethrough may be passed through the tubing. Such adrift member may be pumped through the tubing relatively quickly. If norestriction is encountered, the tubing may then be retrieved. However,if the presence of a restriction is identified, a second drift memberadapted to prevent or significantly restrict fluid flow is then passedthrough the tubing, typically at a slower rate than the first driftmember. Of course the second drift member will encounter and be stoppedin the tubing by the first drift member. The location of the restrictionmay then be identified, by reference to the volume of fluid pumped intothe tubing behind the second drift member, such that only a limitedlength of the tubing string need be checked for the presence ofrestrictions.

Preferably, engagement of the drift member with the profile restrictsfluid flow through the tubing, which restriction is remotely detectable.Where the tubing extends downhole, engagement of the member with theprofile may be identified as a rise in pump pressure at surface.

Preferably, the drift member comprises a sleeve or the likeincorporating a flow restriction, such as a nozzle or orifice, adaptedto create a fluid pressure differential in fluid passing therethrough.The flow restriction may comprise a hardened or otherwiseerosion-resistant material.

It should be noted that any hollow sleeve would produce a restrictionupon landing on a restriction or profile. However, in order to be usefulin the preferred environment of the present invention the sleeve mustcreate a noticeable pressure increase, and so the restriction must besignificant. This may be illustrated by way of example: although pipesize can vary greatly, the most common drill pipe size is 5 inchdiameter, which normally comprises sections of pipe each with aninternal diameter of 4.25 inch over most of its length and 2.9 inch atthe pipe connection. This corresponds to a flow area of 14.2 sq-in and6.6 sq-in respectively. A typical mud pump has a maximum workingpressure of 5000 psi and the pumps normally work at about 4000 psi. Themaximum typical flowrate for a drifting situation would be 500 gallonsper minute (1900 LPM). At this rate an operator at surface wouldtypically see a 750 psi increase in pressure from a 0.75 in choke (0.44sq-in), a 235 psi increase from a 1.0 in choke (0.79 sq-in), or a 45 psiincrease with a 1.5 in choke (1.76 sq-in). If the operator were onlyable to pump at half this rate the corresponding pressures increaseswould be only one quarter, that is 188 psi, 59 psi & 12 psirespectively. It will be clear from this example that if a clear andunambiguous pressure increase is required on a 5000 psi scale pressuregauge to confirm a good drift, the choke must be of a known andsignificantly smaller internal diameter than the pipe minimum diameter.Thus, a simple hollow sleeve is unlikely to create a pressure increaseat surface of sufficient magnitude to be is easily and reliablyidentified.

Preferably, the drift member is adapted to be retrievable from thetubing. The member may incorporate a profile, more particularly afishing profile, to facilitate withdrawal of the member from the tubing.

The tubing profile may be formed integrally with a portion of thetubing, for example the tubing may incorporate a section or sub thatdefines the profile. Most preferably, the profile may be defined by amember, such as a ring or sleeve, adapted to be located within a sectionof tubing, which section of tubing may be adapted to receive the member.Such a profile member may thus be removed and replaced when worn ordamaged, or when it is desired to employ a different form of driftmember, more particularly a drift member of different dimensions.Alternatively, the profile may be defined by a member adapted forlocation in conventional tubing, the member preferably adapted forlocation at a connection between tubing sections, particularly in afemale or box connection. The profile member will thus be readilyaccessible when the tubing is disassembled, and may be located in atubing string at an appropriate location while the string is being madeup. Conveniently, the profile member may be located in a stress reliefprofiled section of a box connection.

When the drift member engages the profile member, the velocity of thedrift member and the momentum of the fluid following behind the driftmember are likely to be such that profile member will be struck withconsiderable force. Indeed, in one embodiment of the invention it hasbeen estimated that a five tonne force is exerted on the profile memberwhen the drift member lands on the profile. In such circumstances theprofile member may be forced into tight engagement with the tubing andthus subsequent removal of the profile member from the tubing may bedifficult. To this end, the profile member may include a profile or thelike adapted to engage a tool or device to facilitate removal of theprofile member from the tubing.

The profile member may be adapted to form a seal with the tubing.

The drift member may define a profile adapted to engage with the tubingprofile. Preferably, the drift member comprises a body and the profileis removably mounted thereon. Thus, a drift member may be readilymodified to define a different diameter by replacing the drift profile.Also, a worn or damaged drift profile may be readily replaced.

The drift member may be adapted to form a seal with the profile, suchthat any fluid flowing through the tubing when the drift member isengaged in the profile must flow through the drift member. This willensure the presence of a predictable or predetermined pressure drop whenthe drift member is correctly located in the profile, facilitatingdifferentiation from occasions when the drift member encounters and isrestrained by a restriction in the tubing before reaching the profile.

In one embodiment, the drift member may define one or more flow portsspaced from the leading end of the member. For example, where the driftmember comprises a sleeve, the one or more ports may be provided in thesleeve wall. Thus, if the leading end of the sleeve encounters andengages a restriction fluid may flow through the annulus between thetrailing end of the sleeve and the tubing, through the flow ports andinto the interior of the sleeve, and then through the leading end of thesleeve. This minimises the likelihood of the drift member engaging withan obstruction being mistaken for the drift member engaging the profile.In a preferred embodiment, the drift member comprises a sleeve having anexternal profile and defining an internal flow restriction. In such anapparatus, the flow ports may be located in the sleeve wall forwardly ofthe internal flow restriction and the profile.

According to another aspect of the present invention there is provided amethod of checking for restrictions in a length of tubing, the methodcomprising:

passing a drift member through the tubing; and

identifying the location of the drift member in the tubing.

The location of the drift member may be identified remotely, asdescribed above; that is, by utilising a drift member adapted to preventor significantly reduce fluid flow through the tubing. If the driftmember encounters a restriction, the location of the restriction may beidentified by determining the volume of fluid that has been pumped intothe tubing behind the drift member. Preferably, this drift would have arupture disc, or other means to allow the fluid to drain while pullingthe pipe after the position of the obstruction has been located.

Alternatively, the drift member may be simply and practically adapted tobe readily detectable to an operator as the tubing is retrieved, oralternatively by an appropriate sensor. Thus, the tubing may beretrieved without the requirement to check for restrictions orobstructions until the presence of the drift member is detected, atwhich point the obstruction can be removed or the section of pipe withthe obstruction can be removed from the string. In one embodiment thismay be achieved by attaching a tail to the drift member, preferably astiff tail, the tail most preferably being made up of shorter, smallerdiameter interconnected sections of flexible rod or pipe that can beeasily handled. Preferably, the tail would be of relatively lightweightmaterial to facilitate handling of the assembled apparatus and to avoidor minimise damage as the apparatus member travels through the tubing.Alternatively, the drift member could be fitted with an audiblesignalling device, such as a bell provided with a hydrostatic controlswitch. The signalling device could be battery powered or mostpreferably clockwork, such that when the drift member came to surface,where there is no hydrostatic pressure, the bell sounds, alertingpersonnel to the presence of the drift member in the pipe.

In certain embodiments the drift member may comprise a radioactivesource, detectable by means of a Geiger counter or the like.Alternatively, the drift member may comprise a radio transmitter, thesignals from the transmitter being detected by an appropriate receiver.In other embodiments, the drift member may include means for producingan electromagnetic or electrical output, or simply a magnetic member, orindeed any form of output or signal that is detectable externally of thetubing. However, as these embodiments require the provision of dedicateddetection apparatus, with the associated cost and potentialinconvenience, it is anticipated that operators will prefer solutionssuch as the bell described above.

In other embodiments, the location of the drift member may be identifiedfrom surface immediately following landing of the drift member on anobstruction. For example, the tubing or surrounding bore-lining casingmay incorporate sensors capable of identifying the drift member locationand transmitting the appropriate information to surface.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be described, by wayof example, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of apparatus for identifying borerestrictions in tubing, in accordance with an embodiment of the presentinvention and showing a drift member located externally of a profiledsub;

FIG. 2 is an enlarged sectional view of the drift member of FIG. 1;

FIG. 3 is a sectional view of apparatus for identifying borerestrictions in tubing, in accordance with a further embodiment of theinvention;

FIG. 4 is a sectional view of apparatus for identifying borerestrictions in tubing in accordance with a still further embodiment ofthe present invention;

FIG. 5 is an enlarged sectional view of the drift member of FIG. 4; and

FIGS. 6 a and 6B are sectional views of apparatus for identifying borerestrictions in accordance with a yet further embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIG. 1 of the drawings, which illustratesapparatus for use in identifying bore restrictions in tubing, inaccordance with an embodiment of the present invention. The apparatus 10comprises a sub 12 and a drift member in the form of a drift sleeve 14adapted to engage within the sub 12, as will be described.

The sub 12 is intended for incorporation in the lower end of a string ofconventional drill pipe, and thus incorporates conventional pin and boxconnections 16, 17, and defines a central through bore 18. However, thebore 18 defines a profile in the form of a shoulder 20 arranged toreceive and engage the drift sleeve 14, which is illustrated externallyof the sub 12 in FIG. 1.

The drift 14 is illustrated in greater detail in FIG. 2 of the drawings,and comprises a generally cylindrical body 22 with a slightly taperedleading end 24, whereas the trailing end 26 defines an external profile28 for co-operation with the sub shoulder 20 and an internal fishingprofile 30. An internal ledge 32 within the sleeve body 22 supports ahardened nozzle ring 34 that is in sealing engagement with the innerwall of the sleeve body 22.

Radial flow ports 36 are provided in the body 22, between the leadingend 24 and the nozzle ring 34.

In use, as a pipe string is made up and lowered into a drilled bore, thesub 12 is incorporated in the string, at or towards the leading ordistal end of the string. Once the operation requiring use of the stringhave been completed, and before the string is pulled out of the bore anddisassembled, the drift sleeve 14 is inserted into the string bore atsurface and pumped down through the string. If the string bore issubstantially free from obstruction or restriction, the sleeve 14 willpass down through the string until it encounters the drift sub 12, wherethe sleeve profile 28 will engage the sub shoulder 20 and preventfurther travel of the sleeve 14. The sub bore 18 and the sleeve externalconfiguration are such that the sleeve 14 is substantially a sealing fitwithin the sub 12, such that any fluid passing through the string fromsurface must then pass through the nozzle 34, and will thereforeexperience a pressure drop. The restriction introduced into the stringbore by the nozzle 34 is reflected at surface by a readily identifiableincrease in pump pressure, which indicates to the operators on surfacethat the sleeve 14 has engaged within the sub 12, and that the pipestring is substantially free of obstruction and restriction.

However, where the pipe string has been restricted or obstructed by, forexample, cement residue, the sleeve 14 will not be able to pass therestriction to reach and engage with the sub 12. In such circumstances,the sleeve 14 will of course still create a flow restriction in the pipestring bore, however the leading end 24 will land on the restriction inthe pipe but the sleeve 14 will not sealingly engage with the pipe suchthat fluid will flow around as well as through the sleeve 14. If theleading end 24 should encounter an annular pipe restriction, preventingflow between the exterior of the leading end 24 and the pipe wall, fluidmay still pass through the flow ports 36. Thus, while the engagement ofthe sleeve 14 with a restriction may be reflected in an increase in pumppressure at surface, this increase will be noticeably less than thepressure increase that would be expected if the sleeve 14 were to engageand locate within the drift sub 12. Accordingly, the operators are thenalerted to the fact that the string bore is restricted or obstructed. Inthis case, which it is expected will occur in perhaps one in ten runs ofa drift sleeve 14, the pipe string can be checked for obstructions on astand-by-stand basis, in a conventional manner, as described above.Alternatively, the sleeve 14 may be used in conjunction with a furtherdrift sub as will be described subsequently, with reference to FIGS. 4and 5.

Of course, in the perhaps nine out of ten cases in which the driftsleeve 14 passes through the string to engage within the drift sub 12,it is not necessary for the operator to check the string bore as thestring is disassembled on surface, providing a significant saving intime and thus expense.

Reference is now made to FIG. 3 of the drawings, which illustratesapparatus 40 for use in identifying bore restrictions in tubing, inaccordance with a further embodiment of the invention. The apparatus 40is substantially similar to the apparatus 10 described above, however,rather that incorporating an integral profile or shoulder 20, as in thedrift sub 12, the drift sub 42 of this embodiment is provided with aninsert 44 that defines an internal profile 46 adapted to engage acorresponding profile 48 on the drift sleeve 50. The insert 44 sits on aledge 52 defined within the sleeve bore and also carries external seals54 to ensure that no fluid passes between the sleeve 44 and the sub borewall.

The provision of an insert 44 allows the profile 46 to be modified tosuit different drift sleeve configurations, and of course the insert 44may be replaced in case of erosion or damage.

Furthermore, the drift sleeve 50 of this embodiment includes an audiblesignalling device, in particular a clockwork bell 56 provided with ahydrostatic control switch, such that when the drift sleeve 50 comes tosurface, where there is no hydrostatic pressure, the bell sounds,alerting personnel to the presence of the drift sleeve 50 in the pipe.

The ringing of the bell 56 will alert the operators to the presence ofthe sleeve 50 in a stand of pipe, such that the stand may then bechecked for the presence of an obstruction. Of course, it will not havebeen necessary to check any of the preceding stands for the presence ofthe sleeve 50 and a corresponding string bore restriction orobstruction.

Reference is now made to FIGS. 4 and 5 of the drawings, which illustrateapparatus for identifying bore restrictions in tubing in accordance witha still further embodiment of the present invention. In this embodiment,there is no requirement to provide a specially adapted drift sub, as theprofile 60 for engaging with the drift member, in this example in theform of a cylindrical drift dart 62, is adapted to be located within aconventional pipe section, and in particular within the “bore back” boxconnection 64 of a pipe section 66. This particular form of box is acommon feature on pipe sections, intended to reduce fatigue at theconnection.

The profile 60 is defined by a nozzle ring 68 which may be locatedwithin the box connection 64 during the make-up of the pipe string, thering 68 forming a sealing fit with the inner wall of the connection 64.

The drift dart 62 comprises a generally cylindrical body 70 having atapering leading end 72 and defining an external profile 74 adjacent theleading end 72, for engaging with the profile 60. The trailing end 76incorporates a burst disc 78 and features external flexible fins 80 thatassist in stabilising the dart 62 as it is pumped through the tubingstring.

In use, the dart 62 is inserted into the tubing string bore at surfaceand is then pumped down through the string. If there are no significantbore restrictions or obstructions the dart 62 will pass through thestring until it engages with the profile 60. This will be reflected by asharp increase in pump pressure at the surface, which will be readilydetectable by the operators. By identifying the volume of fluid that hasbeen pumped into the string bore behind the dart 62, it is possible toconfirm that the dart has reached the profile 60, as the location of theprofile 60 is known. By increasing the pump pressure further theoperators may burst the disc 78, such that fluid may drain from thetubing string as it is withdrawn and dismantled.

If, on the other hand, the dart 62 encounters a restriction orobstruction before reaching the profile 60, there will be a similarincrease in pump pressure at surface. However, as the dart 62 has nottravelled as far as it would in the absence of the restriction orobstruction, the volume of fluid pumped into the string bore will beless than that which would be expected were the dart 62 to pass all theway through the pipe string and engage with the profile 60. Accordingly,the operators will be alerted to the fact that there is a restriction oran obstruction in the string bore. Furthermore, the volume of fluidpumped into the bore will provide an indication of the location of theobstruction in the string such that the bore need not be checked as thestring is pulled out of the bore until approaching the anticipatedlocation of the dart 62 in the string.

This embodiment thus offers the advantage, over the embodiment of FIGS.1 and 2, of providing an indication of the location of the obstructionand thus reducing the number of pipe stands that need to be checked forobstructions at surface. However, to prevent bursting the disc 78immediately on encountering a restriction, or the profile 60, the dart62 must be pumped into the string relatively slowly, and thus may takesignificantly longer to travel through the string. Accordingly, in somesituations, operators may choose to check for restrictions in a pipestring by first pumping down a drift sleeve 14, as illustrated in FIG.2, which operation may be carried out relatively rapidly. If the sleeve14 passes all the way through the string to engage with a drift sub 12,no further action is necessary, and the string may be retrieved anddismantled. However, if an obstruction is identified (which is the casein perhaps 5-10% of cases), the drift dart 62 is then pumped into thepipe string. The drift dart 62 will pass down through the string untilit encounters the drift sleeve 14, and by noting the volume of fluidpumped down behind the dart 62, the location of the dart in the string,and thus the location of the restriction, may be determined.

Running the drift sleeve 14 is a relatively rapid means for determiningthe presence of a string bore restriction or obstruction, and in thosecases where an obstruction is identified, running the drift dart 62allows the location of the obstruction to be determined. The additionaltime involved in running the drift dart 62 is more than compensated forby the saving in time made when retrieving and disassembling the string:the pipe stands need not be checked for the presence of obstructionsuntil the section of the string in which the drift members 14, 62 arelocated is brought to surface.

Reference is now made to FIGS. 6 a and 6 b of the drawings, which aresectional views of apparatus 110 for identifying bore restrictions inaccordance with a yet further embodiment of the present invention. Theapparatus 110 comprises a drift member in the form of an elongate driftrod 111 having a stabilising sleeve 114 b at its leading end and a driftsleeve 114 a at its trailing end.

The drift sleeve 114 a comprises a generally cylindrical two-part body122 a carrying a replaceable drift profile 124 a. The upper free end ofthe drift sleeve 114 a defines a fishing neck 130, to facilitateretrieval of the apparatus 110, if required. The sleeve leading enddefines a threaded male profile 128 a for co-operation with the upperend of the drift rod 111. The body 122 a has an open upper end leadinginto a bore 123 a which permits the flow of fluid through the body 122a, the fluid entering or exiting the lower end of the bore 123 a via tworadial flow ports 125 a.

The drift rod is formed of a number of composite rod sections. The rodsections are of a length and weight selected to facilitate handling andare joined together to provide a rod 111 approximately 100 feet long.The rod sections may be formed of any appropriate material, such as apolymeric material, a composite or a lightweight metal alloy, and definea smaller diameter than the drift and stabilising sleeves 114 a,b. Therod sections are sufficiently stiff such that the sections areself-supporting but do permit a degree of flex, thus facilitatinghandling and passage of the apparatus through a string.

The leading, stabilising sleeve 114 b is of generally similarconstruction to the drift sleeve 114 a and comprises a generallycylindrical two-part body 122 b carrying a replaceable taperedcentralising/stabilising profile 124 b, defining a slightly smallerdiameter than the drift profile 124 a, the sleeve trailing end defininga threaded male profile 128 b for co-operation with the lower end of thedrift rod 111. The body 122 b has an open leading end and a bore 123 bcommunicating with two radial flow entry ports 125 b.

In other embodiments, different forms of stabilising or centralisingarrangement may be utilised, for example a bow-spring type centraliser.

In use, the diameter to which the string should be 5 drifted will havepreviously been identified; this may be the diameter of a ball, dart orplug it is intended to pass through the string after the string has beenretrieved and then run into the bore once more. The diameters of theprofiles 124 a, 124 b are selected to match this diameter, the trailingdrift profile 124 a typically being selected to be slightly larger thanthe ball, dart or plug diameter, and the leading stabilising profile 124b being slightly smaller (although in some embodiments the diameter ofthe leading profile may be the greater). The pipe string will alsoincorporate an appropriately dimensioned a sub 12, 42 or profile 60. Thesleeves 114 a, 114 b are then assembled and made up to the ends of thedrift rod 111, which has been formed by joining the rod sectionstogether. The assembled drift member is inserted into the string bore atsurface and pumped down through the string, typically just beforeretrieval of the string commences.

If the string bore is substantially free from obstruction orrestriction, the member will pass down through the string until thedrift sleeve 114 a engages a sub 12, 42 or profile 60, as describedabove. The landing of the sleeve 114 a on the sub or profile isidentified from the rise in pump pressure at surface. However, where thepipe string has been restricted or obstructed by, for example, cementresidue, the sleeve 114 a will not be able to pass the restriction. Asnoted above, this may result in a rise in pump pressure at surface, butthe rise will be significantly less than that produced by the sleeve 114a landing on a sub 12, 42 or profile 60. If necessary, the apparatus 110may be retrieved from the pipe string by running an appropriate toolinto the string to engage with the fishing neck 130, the sleeve 114 aensuring that the neck 130 is centralised in the pipe.

As noted above, where the pipe string has been restricted or obstructedthe location of the obstruction can be identified without difficulty asthe string is retrieved and disassembled on a stand-by-stand basis; thedrift rod 111 is longer than a stand of pipe and thus will extend fromthe end of the stand in which the drift sleeve 114 a has landed.

The apparatus 110 may be withdrawn from the obstructed stand of pipe andthe stand put to one side for inspection. The apparatus 110 is thendropped into the remainder of the string still to be retrieved, to checkfor the presence of any further restrictions or obstructions.

The apparatus may also be used in circumstances where a sub 12, 42 orprofile 60 has not been provided in the pipe string. In thesecircumstances the apparatus 110, provided with profiles of appropriatediameter 124 a, 124 b, may simply be dropped into the string, ratherthan pumped through the string. If the string bore is substantially freefrom obstruction or restriction, the member will pass down through thestring until the stabilising sleeve 114 b encounters the upper end ofthe bottom hole assembly (BHA) or some other pre-existing restriction.The relatively light weight of the apparatus 110 is such that theapparatus will not cause any damage to the string as it passestherethrough, and will not damage the BHA when the member lands on anupper part of the BHA.

However, where the pipe string has been restricted or obstructed by, forexample, cement residue, the sleeve 114 a will not be able to pass therestriction. The operator will not be aware whether the apparatus 110has passed through the length of the string or has landed on arestriction, however the apparatus 110 will be immediately visible asthe string is retrieved and disassembled on a stand-by-stand basis,allowing the presence and location of any restriction to be readilyidentified.

It will be apparent to those of skill in the art that theabove-described embodiments of the present invention provide arelatively rapid means for determining whether there is any significantrestriction or obstruction present in a tubing string. The operation maybe carried out easily and safely while the tubing string remains in thebore, and the form of the various drift members is such that in thepresence of a drift member within a string will not interfere orcomplicate the subsequent pulling out and disassembly of the string. Asnoted above, in the great majority of cases where no significantrestriction or obstruction is likely to be identified, the operator maythen disassemble the string with the knowledge that no restrictions orobstructions are present, and the normal checks for restrictions neednot be carried out. Furthermore, a number of embodiments of the presentinvention allow the location of any restriction or obstruction to bedetermined, such that only selected portions of the string need bechecked for the presence of obstructions.

It will also be apparent to those of skill in the art that theabove-described embodiments are merely exemplary of the presentinvention, and that various modifications and improvements may be madethereto without departing from the scope of the invention.

1-69. (canceled)
 70. A method of checking for restrictions in a stringof tubing located in a drilled bore and comprising a plurality of tubingsections, the method comprising: providing a profile in the tubingstring; providing a drift member adapted to engage with said profile;passing the drift member through the tubing string; and determiningwhether the drift member has engaged with said profile prior toretrieving the string from the bore and separating the tubing sections.71. The method of claim 70 comprising the further step of pumping thedrift member through the tubing string.
 72. The method of claim 70,further comprising: pumping the drift member through the tubing from aproximal end of the tubing, to engage a restriction in the tubing; andthen identifying the location of the restriction by identifying thelocation of the drift member in the tubing from said proximal end of thetubing.
 73. The method of claim 70, further comprising permitting fluidto drain from the tubing with the drift member in place.
 74. The methodof claim 70, wherein engagement of the drift member with the profilesignificantly restricts fluid flow through the tubing.
 75. The method ofclaim 70, further comprising reconfiguring the drift member tofacilitate fluid flow through the tubing.
 76. The method of claim 70,further comprising determining the location of a restriction in thetubing engaged by the drift member by identifying a volume of fluidpumped into the tubing behind the drift member.
 77. The method of claim70, wherein engagement of the drift member with a restriction restrictsfluid flow through the tubing, and comprising the further step ofremotely detecting such restriction.
 78. The method of claim 77, whereinengagement of the drift member with the restriction is identified by arise in pump pressure.
 79. The method of claim 70, wherein the profileis located towards a distal end of the tubing string.
 80. The method ofclaim 70, further comprising passing the drift member adapted to permitfluid flow therethrough through the tubing and, if no restriction isencountered by the drift member prior to the profile, retrieving thetubing.
 81. The method of claim 70, further comprising providing thetubing profile integrally with a portion of the tubing.
 82. The methodof claim 70, further comprising providing the tubing profile in the formof a member adapted to be located within a section of tubing. 83.Apparatus for identifying the presence of a bore restriction in a tubingstring located in a drilled bore, the apparatus comprising a driftmember and a profile for location in a tubing string, the drift memberbeing adapted to pass through tubing string from a proximal end of thestring and to engage the profile, wherein the engagement of the driftmember with the profile is operator detectable from the proximal end ofthe tubing.
 84. Apparatus comprising a drift member for identifying thepresence of a bore restriction in a tubing string located in a drilledbore, the drift member being adapted to be pumped through a tubingstring from a proximal end of the string and to engage a profile in thestring, wherein the engagement of the drift member with the profile isoperator detectable from the proximal end of the tubing.
 85. Theapparatus of claim 83, wherein the drift member is adapted to be pumpedthrough the tubing.
 86. The apparatus of claim 83, wherein the driftmember has flexible fins.
 87. The apparatus of claim 83, wherein thedrift member is adapted to permit fluid flow.
 88. The apparatus of claim83, wherein the drift member is in the form of a sleeve.
 89. Theapparatus of claim 83, wherein the drift member is configurable torestrict fluid flow therethrough.
 90. The apparatus of claim 83, whereinthe drift member includes a burst disc.
 91. The apparatus of claim 83,wherein the drift member is configured such that engagement of the driftmember with the profile restricts fluid flow through the tubing, whichrestriction is remotely detectable.
 92. The apparatus of claim 83,wherein the drift member comprises a flow restriction adapted to createa fluid pressure differential in fluid passing therethrough.
 93. Theapparatus of claim 92, wherein the flow restriction is formed of anerosion-resistant material.
 94. The apparatus of claim 83, wherein thedrift member is retrievable from the tubing.
 95. The apparatus of claim83, wherein the tubing profile is formed integrally with a portion oftubing.
 96. The apparatus of claim 83, wherein the tubing profile isdefined by a member adapted to be located within a section of tubing.97. The apparatus of claim 96, wherein the profile member is adapted toform a seal with the tubing.
 98. The apparatus of claim 83, wherein thedrift member defines a drift profile adapted to engage with the tubingprofile.
 99. The apparatus of claim 98, wherein the drift member furthercomprises a body and the drift profile is removably mounted thereon.100. The apparatus of claim 83, wherein the drift member is adapted toform a seal with the tubing profile, such that any fluid flowing throughthe tubing when the drift member is engaged in the profile must flowthrough the drift member.
 101. The apparatus of claim 83, wherein thedrift member is configured such that engagement of the drift member withthe profile restricts fluid flow through the tubing and such thatengagement with a restriction other than the profile restricts fluidflow through the tubing to a lesser extent.
 102. The apparatus of claim101, wherein the drift member comprises flow ports adapted to be closedon engagement of the drift member with the profile and to remain open onengagement of the drift member with a restriction other than theprofile.